1. Field of the Invention
The present invention relates to a device for moving a cam relative to its driving shaft. The invention can be used for a camshaft of an internal combustion engine for varying duration of opening of an intake or exhaust valve or phase of opening and closing of the valve in a dual overhead camshaft internal combustion engine.
2. Description of the Related Art
U.S. Pat. No. 5,365,896 discloses a device for moving a hollow cam relative to its driving shaft that is driven by a crankshaft of an engine for rotation about a shaft axis. The device includes a drive member connected to the driving shaft, a driven member connected to the hollow cam and an intermediate member operatively connected between the drive and driven members. A support has mounted therein the intermediate member. The intermediate member has an axis and a central hole that is wide enough to allow limited movement of the support to vary eccentricity of the axis thereof with respect to the shaft axis. The drive member is coupled with the intermediate member by a first coupling at a first position spaced from the shaft axis. The driven member is coupled with the intermediate member by a second coupling at a second position that is spaced in angular direction with respect to the shaft axis. Each of the first and second couplings has a movable connection with the intermediate member to permit variation in its distance from the axis of the intermediate member during operation. The support is pivoted via a pivot shaft to a framing structure for movement within a plane perpendicular to the shaft axis. The framing structure is fixedly mounted to a cylinder head of the associated engine. To move the support, an actuator rotates via a control rod an eccentric cam that is received in a hole of the support. Both the actuator and control rod are also mounted to the framing structure.
According to the known device, the pivot shaft is needed for the support, thus increasing the number of component parts and requiring increased installation space.
In addition to a bearing structure for the hollow cam, another independent structure is required for supporting the pivot shaft, making it difficult to find installation space above the cylinder head.
The fact that the support is pivoted makes it difficult to adjust the intermediate member with respect to the shaft axis, causing a deviation from a desired valve timing control. This also causes cylinder to cylinder variation in valve timing, increasing probability of occurrence of irregular operation due to cylinder to cylinder variation in power output.
As the hollow cam opens the associated cylinder valve against its valve spring, the reaction is transmitted via the first and second couplings to the intermediate member and then to the support. At only two spaced points, the support must bear stress due to the valve spring. Thus, the support bends at a portion between the two spaced points, causing undesired deviation of the axis of the intermediate member from the shaft axis, causing a deviation from desired valve timing.
U.S. Pat. No. 5,333,579 discloses a known device similar to the device discussed above.
An object of the present invention is to improve the device of the above kind such that the support for the intermediate member is not employed.